Yeah we'll how much does your old man Deadlift? I've always felt you should lower hips to the point were you feel you have maximum leverage off the floor. Any more is a waste an any less is not enough leg drive.

His biggest pull was 725 lbs. He's now 57 and just started PLing again after an 8 year drought and is back in the 500+ DL raw at 6 months in. At the same time of this 725 deadlift he also squatted 655 and benched 505. This is with gear, single ply. He's not too shabby.